Begin adding test for parquet export

Changed logic for handling anonymous edits so that wikiq handles
the type for editor ids consistently. Parquet can mix int64 and
None, but not int64 and strings - previously the code used the empty
string to denote anonymous editors.

Tests failing. Don't merge yet.

Signed-off-by: Will Beason <willbeason@gmail.com>

.gitignore

@@ -9,4 +9,5 @@
 
 # Python build and test output
 __pycache__/
-test_output/
+/test/test_output/
+/test/test_output.parquet/